Protein kinases represent a large family of enzymes, which catalyze the phosphorylation of target protein substrates. The phosphorylation is usually a transfer reaction of a phosphate group from ATP to the protein substrate. Common points of attachment for the phosphate group to the protein substrate include, for example, a tyrosine, serine or threonine residue. Examples of kinases in the protein kinase family include, without limitation, ab1, Akt, Aurora A, Aurora B, Aurora C, bcr-ab1, Blk, Brk, Btk, c-kit, c-Met, c-src, c-fms, CDK1, CDK2, CDK3, CDK4, CDK5, CDK6, CDK7, CDK8, CDK9, CDK10, cRaf1, CSF1R, CSK, EGFR, ErbB2, ErbB3, ErbB4, Erk, Fak, fes, FGFR1, FGFR2, FGFR3, FGFR4, FGFR5, Fgr, flt-1, Fps, Frk, Fyn, Hck, IGF-1R, INS-R, Jak, KDR, Lck, Lyn, MEK, p38, PDGFR, PIK, PKC, PYK2, ros, Tie, Tie2, TRK, Yes, and Zap70. Due to their activity in numerous cellular processes, protein kinases have emerged as important therapeutic targets.
Protein kinases play a central role in the regulation and maintenance of a wide variety of cellular processes and cellular function. For example, kinase activity acts as molecular switches regulating cell proliferation, activation, and/or differentiation. Uncontrolled or excessive kinase activity has been observed in many disease states including benign and malignant proliferation disorders as well as diseases resulting from inappropriate activation of the immune system (autoimmune disorders), allograff rejection, and graft vs host disease. In addition, endothelial cell specific receptor PTKs, such as Tie-2, mediate the angiogenic process and are involved in supporting the progression of cancers and other diseases involving uncontrolled vascularization.
Angiogenesis is the process of developing new blood vessels, particularly capillaries, from pre-existing vasculature and is an essential component of embryogenesis, normal physiological growth, repair, and tumor expansion. Angiogenesis remodels small vessels into larger conduit vessels, a physiologically important aspect of vascular growth in adult tissues. Vascular growth is required for beneficial processes such as tissue repair, wound healing, recovery from tissue ischemia and menstrual cycling.
Certain diseases and/or pathological conditions develop as a result of, or are known to be associated with, the regulation and/or deregulation of angiogenesis. For example, ocular neovascularisation such as retinopathies (including diabetic retinopathy), age-related macular degeneration, psoriasis, hemangioblastoma, hemangioma, and arteriosclerosis have been found to be caused, in part, due the loss of regulation and/or maintenance of vascular growth. Inflammatory diseases such as a rheumatoid or rheumatic inflammatory disease, and especially arthritis (including rheumatoid arthritis) where new capillary blood vessels invade the joint and destroy cartilage, have been associated with angiogenesis. In addition, chronic inflammatory disorders such as chronic asthma, arterial or post-transplantational atherosclerosis, endometriosis, and neoplastic diseases including so-called solid tumors and liquid tumors (for example, leukemias), have been found to be linked to the regulation and control of angiogenesis.
The involvement of angiogenesis in major diseases has led to the identification and development of various targets for inhibiting angiogenesis. One target identified in the cascade of events leading to angiogenesis is the Tie receptor family. The Tie-1 and Tie-2 receptors are single-transmembrane, tyrosine kinase receptors (Tie stands for tyrosine kinase receptors with immunoglobulin and EGF homology domains). Tie-2 is an endothelial cell specific receptor tyrosine kinase, which is involved in angiogenic processes, such as vessel branching, sprouting, remodeling, maturation and stability. Tie-2 is the first mammalian receptor for which both agonist ligand(s) (for example, Angiopoietin-1 (“Ang1”) which binds to and stimulates phosphorylation and signal transduction of Tie-2), and context dependent agonist/antagonist ligand(s) (for example, Angiopoietin-2 (“Ang2”)) have been identified. Knock out and transgenic manipulation of the expression of Tie-2 and its ligands indicates that tight spacial and temporal control of Tie-2 signaling is important for the proper development of new vascularization.
Biological models suggest that the stimulation of Tie-2 by the Ang1 ligand is directly involved in the branching, sprouting and outgrowth of new vessels, and recruitment and interaction of periendothelial support cells important in maintaining vessel integrity and inducing quiescence. The absence of Ang1 stimulation of Tie-2 or the inhibition of Tie-2 autophosphorylation by Ang2, which is produced at high levels at sites of vascular regression, may cause a loss in vascular structure and matrix contacts resulting in endothelial death, especially in the absence of growth/survival stimuli.
Recently, upregulation of Tie-2 expression has been found in the vascular synovial pannus of arthritic joints of humans, consistent with the role in inappropriate neovasculariation. This finding suggests that Tie-2 plays a role in the progression of rheumatoid arthritis. Point mutations producing constitutively activated forms of Tie-2 have been identified in association with human venous malformation disorders. Tie-2 inhibitors would, therefore, be useful in treating such disorders, as well as in other instances of improper neovasacularization. However, with the recent recognition of Ang3 and Ang4 as additional Tie-2 binding ligands, targeting a Tie-2 ligand-receptor interaction as an anti-angiogenic therapeutic approach is less favorable. Accordingly, a Tie-2 receptor kinase inhibition approach has become the strategy of choice.
The inhibition of vascular growth in this context has also shown beneficial effects in preclinical animal models. For example, inhibition of angiogenesis by blocking vascular endothelial growth factor or its receptor has resulted in inhibition of tumor growth and in retinopathy. Also, the development of pathological pannus tissue in rheumatoid arthritis involves angiogenesis and might be blocked by inhibitors of angiogenesis.
The ability to stimulate vascular growth has potential utility for treatment of ischemia-induced pathologies such as myocardial infarction, coronary artery disease, peripheral vascular disease, and stroke. The sprouting of new vessels and/or the expansion of small vessels in ischemic tissues prevents ischemic tissue death and induces tissue repair. Regulating angiogenesis by inhibiting certain recognized pathways in this process would, therefore, be useful in treating diseases, such as ocular neovascularization, including retinopathy, age-related macular degeneration, psoriasis, hemangioblastoma, hemangioma, arteriosclerosis, inflammatory disease rheumatoid arthritis, chronic inflammatory disorders such as chronic asthma, arterial or post-transplantational atherosclerosis, endometriosis, and neoplastic diseases such as leukemias, otherwise known to be associated with deregulated angiogenesis.
Another mechanism by which cancerous cells are propagated is by unregulated cell proliferation. Damage to one or more genes, responsible for the cellular pathways, which control progress of proliferation through the cell cycle, typically causes the loss of normal regulation of cell proliferation. These genes code for various proteins, which participate in a cascade of events, including protein phosphorylation, leading to cell-cycling progression and cell proliferation.
One class of proteins found to play a part in cell cycling and, therefore, cell proliferation is the Aurora kinase family of proteins. Aurora kinases are enzymes of the serine/threonine kinase family of proteins, which play an important role in protein phosphorylation during the mitotic phase of the cell cycle. There are three known members of the Aurora kinase family, Aurora A, Aurora B and Aurora C, also commonly referred to as Aurora 1, Aurora 2, and Aurora 3, respectively.
The specific function of each Aurora kinase member in mammalian cell cycle has been studied. Aurora-A is localized to the centrosome during interphase and is important for centrosome maturation and to maintain separation during spindle assembly. Aurora-B localizes to the kinetochore in the G2 phase of the cell cycle until metaphase, and relocates to the midbody after anaphase. Aurora-C was thought to function only in meiosis, but more recently has been found to be more closely related to Aurora-B, showing some overlapping functions and similar localization patterns in mitosis. Each aurora kinase appears to share a common structure, including a highly conserved catalytic domain and a very short N-terminal domain that varies in size. (See R. Giet and C. Prigent, J. Cell. Sci., 112:3591-3601 (1999)).
Aurora kinases appear to be viable targets for the treatment of cancer. Aurora kinases are overexpressed in various types of cancers, including colon, breast, lung, pancrease, prostate, bladder, head, neck, cervix, and ovarion cancers. The Aurora-A gene is part of an amplicon found in a subset of breast, colon, ovarian, liver, gastric and pancreatic tumors. Aurora-B has also been found to be overexpressed in most major tumor types. Overexpression of Aurora-B in rodent fibroblasts induces transformation, suggesting that Aurora-B is oncogenic. More recently, Aurora-B mRNA expression has been linked to chromosomal instability in human breast cancer. (Y. Miyoshi et al., Int. J. Cancer, 92:370-373 (2001)). Further, inhibition of Aurora has been found to arrest cell cycling and promote programmed cell death via apoptosis. Accordingly, there has been a strong interest in finding inhibitors of Aurora kinase proteins.
Many classes of compounds have been proposed to treat cancerous conditions and disorders, including publications disclosing compounds to modulate or specifically inhibit Tie-2 or Aurora kinase activity. For example, WO 04/030635 describes various classes of compounds as vasculostatic agents; WO 04/013141 describes condense pyridines and pyrimidines with Tie-2 activity; WO 04/054585 describes anilino-substituted heterocyclic compounds for the treatment of abnormal cell growth; U.S. Pat. No. 6,395,733 describes heterocyclic ring-fused pyrimidine derivatives, useful in the treatment of hyperpoliferative diseases; U.S. Pat. No. 6,465,449 describes heteroaromatic bicyclic derivatives useful as anticancer agents; U.S. Patent Publication No. 2003/0018029 describes heterocyclic compounds useful in the treatment of poliferative diseases such as cancer; WO 04/039774 describes aza-quinazolinones for treating cancer via inhibition of Aurora kinase; WO 04/037814 describes indazolinones for treating cancer via inhibition of Aurora-2 kinase; WO 04/016612 describes 2, 6, 9-substituted purine derivatives for treating cancer via inhibiton of Aurora kinase; WO 04/000833 describes tri- and tetra-substituted pyrimidine compounds useful for treating Aurora-mediated diseases; WO 04/092607 describes crystals useful for screening, designing and evaluating compounds as agonists or antagonists of Aurora kinase and U.S. Pat. No. 6,919,338 and WO 03/055491 each describe substituted quinazoline derivatives as inhibitors of Aurora-2 kinase. Inspite of the current attempts at finding an anti-cancer therapeutic, there remains a need to find improved, more effective anti-cancer therapies.